Pulse-amplitude modulation, acronym PAM, is a form of signal modulation where the message information is encoded in the amplitude of a series of signal pulses.

Example: A two bit modulator (4-PAM) will take two bits at a time and will map the signal amplitude to one of four possible levels, for example −3 volts, −1 volt, 1 volt, and 3 volts.

Demodulation is performed by detecting the amplitude level of the carrier at every symbol period.

Pulse-amplitude modulation is now rarely used, having been largely superseded by pulse-code modulation, and, more recently, by pulse-position modulation.

In particular, all telephone modems faster than 300 bits/s use quadrature amplitude modulation (QAM). (QAM uses a two-dimensional constellation).

See also

• Pulse-code modulation
• Pulse-position modulation
• Pulse-width modulation
• Pulse-density modulation
• Pulse forming network
• quadrature amplitude modulation